The present invention generaly relates to video signal recording and reproducing apparatuses, and more particularly to a video signal recording and reproducing apparatus having a time lapse mode in which a magnetic tape is transported intermittently and a video signal is recorded on and reproduced from the magnetic tape by use of rotary magnetic heads while the magnetic tape is stationary.
Conventionally, as one kind of helical scan type magnetic recording and reproducing apparatus (hereinafter referred as a video tape recorder or simply VTR), there is the so-called time lapse VTR. The time lapse VTR has time lapse modes in which a magnetic tape is transported at tape speeds different from those used in standard modes of an existing standardized VTR. In the time lapse recording mode of the time lapse VTR, the magnetic tape is continuously transported at a slow speed or is transported intermittently so as to record the video signal by field sampling. As a result, it is possible to record the video signal up to 240 hours, for example, by use of a magnetic tape which is designed to provide two hours of play in the standard mode of the standardized VTR.
The time lapse VTR is used for detailed analysis by reproducing the recorded video signal, or for storing specific reproduced still pictures for a long period of time. Hence, the time lapse VTR is suited for use in a monitoring system such as a security system, a system for operation analysis or recording the circulation of goods, a system for recording broadcasted programs in a television broadcasting station, a system for recording and analyzing observation data obtained in a research center for an extended period of time, and the like.
In the time lapse VTR, it is possible to transport the tape intermittently and record the video signal on the intermittently transported magnetic tape by use of rotary magnetic heads in the so-called still picture recording mode.
However, according to the time lapse VTR of a first type (hereinafter referred to as a first time lapse VTR), a pair of rotary magnetic heads are mounted at diametrical positions on a rotational plane of a rotary body at the same height position along the axial direction of the rotary body. For this reason, in the still picture recording mde, scanning loci of the pair of rotary magnetic heads are identical on the magnetic tape, and it is only possible to form and record the video signal on one track. In order to successively form tracks on the magnetic tape, the video signal amounting to one field must be recorded on one track of the stationary magnetic tape, the magnetic tape must be transported a distance of one track pitch and stopped, and the video signal amounting to another one field must be recorded on the next one track of the stationary magnetic tape. In other words, the magnetic tape must be transported intermittently in the still picture recording mode, and the video signal amounting to one field is recorded on one track and the video signal amounting to another field is recorded on the next one track, where the other field occurs a predetermined time after the one field. Such intermittent tape transport and recording of the video signal on the track of the stationary magnetic tape are repeated in the still picture recording mode. Since the distance of one track pitch is an extremely short distance, the intermittent tape transport must be controlled with an extremely high accuracy. But in actual practice, there is a problem in that it is extremely difficult to carry out the control with such a high accuracy due to inertia of a motor and the like.
On the other hand, there is the time lapse VTR of a second type (hereinafter referred to as a second time lapse VTR) which transports the magnetic tape intermittently between recordings and records the video signal while the magnetic tape is transported at a slow tape speed in the still picture recording mode. In the still picture recording mode of this second time lapse VTR, the pair of rotary magnetic heads successively record the video signal on a pair of successive tracks of the magnetic tape which is transported at the slow tape speed, and the magnetic tape is then stopped. Such intermittent tape transport and recording of the video signal on the pair of successive tracks of the slowly transported magnetic tape are repeated in the still picture recording mode. Hence, a video signal amounting to two fields or one frame is recorded on each pair of successive tracks. Compared to the first time lapse VTR which records the video signal amounting to one field on each track in one recording operation, the second time lapse VTR can obtain a reproduced picture having a vertical resolution two times that obtainable in the first time lapse VTR because the video signal amounting to one frame is recorded on each pair of successive tracks in one recording operation. However, this means that the tape utilization efficiency is one-half that of the first time lapse VTR. Furthermore, in the second time lapse VTR, the video signal amounting to one frame recorded on each pair of successive tracks is made up of first video information amounting to one field and second video information amounting to one field having a time difference of 1/60 sec with the first video information, and the correlation between the first and second video information is extremely high. As a result, there is also a problem in that the recording density obtainable in a predetermined time period is essentially one-half that obtainable in the same predetermined time period on the first time lapse VTR.
On the other hand, it would be very useful if the magnetic tape recorded on the time lapse VTR were compatibly playable on the existing standardized VTR and vice versa. In this case, it would be unnecessary to design a special apparatus exclusively for playing the magnetic tape recorded on the time lapse VTR.
In order to make the track pattern on the magnetic tape recorded on the time lapse VTR compatibly playable on the standardized VTR, the pair of rotary magnetic heads of the time lapse VTR must have gaps of mutually different azimuth angles. But since the magnetic tape is stationary in a still picture reproduction mode of the standardized VTR, it is impossible to obtain reproduced outputs from both rotary magnetic heads of the standardized VTR in the case of the magnetic tape recorded on the first time lapse VTR. It is possible to conceive such an arrangement in the first time lapse VTR that one of the rotary magnetic heads has a wider track width than the other so that the reproduced outputs are obtainable from both the rotary magnetic heads of the standardized VTR. However, in this case, the magnetic tape recorded in a standard recording mode of the first time lapse VTR will be non-compatible with the standardized VTR because of the different track widths of the rotary magnetic heads. In other words, it is impossible to make the magnetic tape recorded on the first time lapse VTR compatibly playable on the standardized VTR regardless of the recording mode used in the first time lapse VTR.
In addition, since the magnetic tape is stationary in the still picture reproduction mode of the standardized VTR, scanning loci of the rotary magnetic heads in the still picture reproduction mode are different from those in the still picture recording mode of the second time lapse VTR in which the magnetic tape is transported at the slow tape speed. Hence, there is a problem in that the picture quality of the reproduced still picture becomes deteriorated due to the difference in scanning loci of the rotary magnetic heads between the still picture recording mode and the still picture reproduction mode of the standardized VTR. Thus, it is impossible to make the magnetic tape recorded on the second time lapse VTR compatibly playable on the standardized VTR regardless of the recording mode used in the second time lapse VTR.